Second pressure-reducing stage for underwater use equipped with a bypass duct and method for making same

ABSTRACT

A second pressure-reducing stage for underwater use includes a supply duct of a breathable gas, in which a valve of a pressure reducing device to reduce the pressure of the breathable gas is provided, the valve being interposed between an inlet of the supply duct and a suction/exhalation mouth to suction/exhale the breathable gas; a casing containing a pressure-sensitive device to control the opening/closing of the valve, the supply duct and the suction/exhalation mouth leading into the casing; and a bypass duct for supplying at least part of the flow of the breathable gas from the supply duct, downstream of the valve, directly into the suction/exhalation mouth, the by-pass duct joining the suction/exhalation mouth through an opening having an axis oriented in a direction which converges towards the axis of the suction/exhalation mouth.

Object of the present invention is a second pressure-reducing stage for underwater use equipped with a bypass, the second stage comprising

a supply duct of a breathable gas in which a valve of a pressure reducing device to reduce the pressure of a breathable gas is provided, the valve being interposed between an inlet of said supply duct and a suction/exhalation mouth to suction/exhale said

a casing containing pressure-sensitive means to control the opening/closing of said valve, the supply duct and the suction/exhalation mouth leading into said casing, i.e. being in communication therewith,

a duct, so-called bypass duct, for supplying at least part of the flow of said breathable gas from the supply duct, downstream of said valve, directly into the suction/exhalation mouth.

Air delivering devices or second pressure-reducing stages for underwater use that can be connected to first pressure-reducing stages adapted to reduce high pressure (200-300 bar) of a breathable gas contained within a tank, usually a cylinder, to a preset intermediate value are known, the second stages reducing the pressure of the gas from said intermediate value to a value physiologically suitable for breathing.

U.S. Pat. No. 4,002,166 describes a second pressure-reducing stage equipped with a by-pass duct thanks to which the breathable gas entering as a result of the opening of the reduction valve is conveyed directly to the suction/exhalation mouth from the supply duct, bypassing the inner chamber of the casing.

The second stage provides that the bypass duct, outside the casing, is tangentially connected with the mouth and that inside the mouth there is a deflector with adjustable inclination.

Patent EP 937640 describes a second pressure-reducing stage in which the bypass duct is integrally obtained inside the casing of said second stage. In this case, the by-pass duct, i.e. the axes of the outlets leading into the suction/exhalation mouth and into the supply duct, are oriented tangentially with respect to the axes of said mouth and said supply duct.

Document IT0001410154 of the same owner provides a by-pass duct whose outlet leading into the supply duct is perpendicular to the axis of the supply duct itself. Similarly, the outlet leading into the suction/exhalation mouth is oriented perpendicularly to the axis of said mouth.

The function of the by-pass duct is to generate a flow for supplying breathable gas into the suction mouth, allowing the user to reduce the suction effort and making the breathing gas delivery response such that the user can breathe as much as possible under natural conditions.

The object of the invention is to improve a second pressure-reducing stage for underwater use equipped with a bypass duct, as those described above, so that the gas flow entering and/or the gas flow flowing inside said bypass duct, in particular the flow rate of breathable gas flowing in the direction of the suction/exhalation mouth, can be regulated.

A further object of the present invention is to obtain an improved second pressure-reducing stage, which can be easily and inexpensively manufactured and overhauled.

The invention achieves the purposes described above by means of a second pressure-reducing stage for underwater use comprising:

a supply duct of a breathable gas in which a valve of a pressure reducing device to reduce the pressure of a breathable gas is provided, the valve being interposed between an inlet of said supply duct and a suction/exhalation mouth to suction/exhale said breathable gas,

a casing containing pressure-sensitive means to control the opening/closing of said valve, the supply duct and the suction/exhalation mouth leading into said casing, i.e. being in communication therewith,

a duct, so-called bypass duct, for supplying at least part of the flow of said breathable gas from the supply duct, downstream of said valve, directly into the suction/exhalation mouth,

and wherein

the by-pass duct joins the suction/exhalation mouth through an opening having an axis oriented in a direction which converges towards the axis of said suction/exhalation mouth.

An embodiment provides that the angle enclosed between the axis of the outlet of the by-pass duct leading into the suction/exhalation mouth and the axis of the suction/exhalation mouth is less than 90°, preferably between 90° and 45°.

According to an embodiment the by-pass duct joins the supply duct through an outlet whose axis is oriented at an angle with respect to the axis of the supply duct between 75 and 105°, preferably substantially perpendicular to the axis of said supply duct.

In an embodiment, the supply duct has a longitudinal axis oriented according to a first direction and the suction/exhalation mouth has a longitudinal axis oriented according to a second direction, said first and said second directions being preferably different from each other and crossed to one another,

the by-pass duct having a first connecting section to connect to the supply duct with an axis of the outlet leading into the supply duct oriented transversely to the axis of said supply duct with a predetermined incidence angle, the by-pass duct having a second connecting end-section to connect to the suction/exhalation mouth, the axis of the outlet leading into said suction/exhalation mouth being oriented transversely to the axis of said suction/exhalation mouth with a second incidence angle,

said first section and said second section of the by-pass duct being connected together through one or more intermediate sections having at least two curvatures with two different radii of curvature and according to different directions of curvature.

An advantageous embodiment provides that said reducing second-stage and, in particular, said casing, said supply duct, said suction/exhalation mouth and said by-pass duct are made of plastic.

According to an embodiment, the intermediate sections of the by-pass duct are made to adhere against at least part of the outer wall, at least of the supply duct and/or the suction/exhalation mouth and/or part of the outer wall of the casing provided between the suction duct and the suction/exhalation mouth.

According to an improvement, the walls delimiting the by-pass duct, and at least the supply duct and/or the suction/exhalation mouth and/or the casing are made of the same material and in one piece.

According to a preferred embodiment, the first section of the by-pass duct leads into the supply duct with an opening having an axis perpendicular to the axis of the supply duct, and extends by means of a first straight intermediate section whose axis is parallel to the axis of said supply duct and said opening is connected to said first straight intermediate section with a basically 90° curvature in the direction of the casing,

the second section of the by-pass duct leads into the suction/exhalation mouth through an opening, the opening having an axis oriented at an acute angle with respect to the axis of the suction/exhalation mouth and from which the second section of the by-pass duct branches off, the latter having an axis parallel to that of the opening itself, whereas between said second section of the by-pass duct and said first straight intermediate section there is a second intermediate linking section linked to said second section for the connection to the suction/exhalation mouth and to the first straight intermediate section by means of a respective curved length, said curved lengths having identical or different directions and/or angles and/or radii of curvature.

According to an embodiment, the axis of the supply duct extends on a different plane with respect to the axis of the suction/exhalation mouth, whereas the axis of the second section for the connection to the suction/exhalation mouth is in a plane coincident with the plane containing the axis of said suction/exhalation mouth or whose distance from this plane is different from the distance of the plane containing the axis of the supply duct and said second intermediate section, the axis of the second intermediate section being inclined with respect to said planes, and the curved lengths being made with angular extensions corresponding to said inclination.

Process for manufacturing a second pressure-reducing stage for underwater use equipped with a bypass, the process comprising the steps of:

providing a sacrificial insert whose shape matches at least the inner compartment of the by-pass duct,

placing said sacrificial insert in a mold provided with at least one or more injection nozzles;

providing sacrificial positioning supports for said sacrificial insert;

closing the mold and injecting the forming plastic to form the casing, supply duct and suction/exhalation mouth portions.

An embodiment provides that the sacrificial insert is made to match the shape both of the inner compartment of the by-pass duct and at least part of the inner compartment of the supply duct and/or of the suction/exhalation mouth, said part being provided at least over a certain angular amplitude in a circumferential direction and along a certain axial length at the respective openings leading the by-pass duct into said supply duct and/or into said suction/exhalation mouth.

According to a preferred embodiment, said sacrificial insert comprises a part shaped to match the inner compartment of the by-pass duct as well as a part of the sacrificial insert matching the entire supply duct and a part of the sacrificial insert matching the inner compartment of the suction/exhalation mouth, respectively at the ends of said part matching the inner compartment of the by-pass duct.

Still according to a preferred embodiment, the part of the sacrificial insert matching the entire supply duct and/or the part of the sacrificial insert matching the inner compartment of the suction/exhalation mouth, are made tubular.

According to an embodiment variant of the method, the sacrificial insert is positioned in the forming mold by means of inserts, i.e. protrusions of the mold part which are inserted either inside the part of the sacrificial insert matching the entire supply duct and/or the part of the sacrificial insert matching the inner compartment of the suction/exhalation mouth in order to obtain the tubular shape of said supply duct and/or said suction/exhalation mouth.

Still according to a preferred embodiment said sacrificial insert is made in one piece by injection molding with a plastic material that can be removed by solution, in particular and preferably water-soluble.

Examples of this plastic material are:

water-soluble resins of the alkyl group, polyvinyl alcohol (pvoh), water-soluble salts, such as for example sodium chloride or potassium chloride or other resins and/or water-soluble polymers.

According to a still further embodiment, the process provides that a plurality of injection nozzles of the plastic material for forming the casing, the supply duct, the suction/exhalation mouth and the by-pass duct are arranged so as to be spread along the extension of said by-pass duct.

An embodiment variation provides that the plastic material is fed through said injection nozzles at different times according to a predetermined time sequence.

Thanks to the present invention, the flow of breathable gas injected by the by-pass duct into the suction/exhalation mouth can be oriented according to a converging direction with relatively small angles with respect to the direction in said mouth of the main flow, which on the contrary comes from a chamber in the casing. The incoming flow from the by-pass duct has a component parallel to the main flow in said mouth which is greater than the component transverse to the direction of said main flow, so that it generates a sort of venturi effect that operates so as to carry the main flow and also to exert a further component of force on the compensation membrane that operates the actuating members of the valve, i.e. the opening lever thereof.

The fluid-dynamic conditions in the breathing apparatus are therefore improved, so that the breathing apparatus is made “softer”, i.e. the delivery of breathable gas is made more similar to the natural conditions for the human being.

These and other characteristics and advantages of the present invention will be more evident from the following description of some exemplary embodiments depicted in the attached drawings wherein:

FIG. 1 shows a perspective view of the body of the second pressure-reducing stage equipped with by-pass, according to the present invention.

FIG. 2 is a sectional view of the body of the second stage according to FIG. 1 and along a plane perpendicular to the axis of the suction/exhalation mouth and containing the axis of the supply duct, as well as a section of the by-pass combined with said supply duct.

FIG. 3 is a sectional view of the body of the second stage according to FIG. 1 and along a plane that is parallel to the plane containing the axis of the suction/exhalation mouth and cutting the by-pass section connecting to said mouth and that is parallel to the plane containing the axis of said section of the by-pass or of the outlet leading the by-pass into the suction/exhalation mouth.

FIG. 4 shows a phantom view of the body of the second stage with a first embodiment of a sacrificial insert that is inserted in the compartment defined by the by-pass duct and has the same shape as said compartment.

FIGS. 5 and 6 show, similarly to FIG. 4, a second embodiment variation of the sacrificial insert which, at the ends of the insert portion related to the bypass-duct compartment, comprises an end portion matching the shape of the suction/exhalation mouth and of the supply duct, respectively, along a certain axial length and over a certain circumferential extent, relative to the region of the outlet of the by-pass duct leading into said mouth and into said supply duct.

FIG. 7 shows a third embodiment variation of a sacrificial insert seen from the side of the insert portion shaped to match the inner compartment of the supply duct.

FIGS. 8 to 21 show various overmolding steps of the sacrificial insert of FIG. 7 for manufacturing a body of a second-stage regulator according to FIG. 1.

FIG. 22 shows the third embodiment variation of the sacrificial insert of FIG. 7 but with a view on the opposite side.

FIGS. 21 to 30 show, in the same way as FIGS. 8 to 21, different forming stages of the body of the second-stage regulator from the side thereof corresponding to that of FIG. 22.

FIGS. 31 to 33 show different views of a second stage made by using the process of FIGS. 7 to 30.

FIGS. 34 and 35 show a second stage equipped with by-pass according to the state of the art.

Referring to FIGS. 34 and 35, a second pressure-reducing stage 1 for underwater use equipped with a bypass duct 101, according to the known art, is shown in the figures.

The function of the second pressure-reducing stage for underwater use is to reduce the pressure of the breathing gas coming from a first pressure-reducing stage and deliver it at ambient pressure depending on the depth where the diver is.

A first pressure-reducing stage for underwater use allows the high pressure of the air contained in the cylinder itself (200-300 bar) to be reduced to an intermediate pressure higher than the ambient pressure by 8/10 bar. Therefore, the second stage, connected to the first stage, allows a further pressure reduction.

As illustrated in FIGS. 34 and 35, said second stage 1 consists of a casing 106 containing pressure-sensitive means to control the opening/closing of a valve of a pressure-reducing device for a breathable gas conveyed into said device through a supply duct 103, such as a so-called hose, from a first pressure-reducing stage (not illustrated) connected to a source of breathable gas, generally a cylinder.

As known, the pressure reducing device of the second stage comprises a hollow cylindrical element 107 or supply mouth, with an inlet 117 for the breathable gas which communicates, through a valve, with a gas supply tube 103 connected to a first pressure-reducing stage (not shown).

As shown in FIG. 35, all or part of the hollow cylindrical element 107 can be provided, on an outer side of the casing 106, as a cylindrical extension of the peripheral wall of the casing itself. Or else, the hollow cylindrical element 107 can be provided integrated in the casing, made as a hollow extension of the casing itself, which extends in radial direction, so that the inlet of the breathable gas of the hollow cylindrical element 107 is made on the wall of the casing 106 itself.

Therefore, for ease of explanation and description, herein the expression “hollow cylindrical element or mouth 107” means both a hollow cylindrical element 107 provided on the outside of the casing 106, as shown in FIG. 35, and a hollow cylindrical element 107 integrated in the casing 106, which is a hollow lateral extension of the casing 106 itself.

At the inlet of the breathable gas, a sealingly fastening end, for example bushing-shaped, can be provided for connecting said supply tube 103 to said hollow cylindrical element or mouth 107.

Inside the hollow cylindrical element 107 a shutter 108 of a valve seat 104 is slidingly assembled, in particular a piston shutter with flared head integrally connected to a stem that engages in a hole provided on a wall opposite the inlet of the breathable gas.

The valve seat 104 consists of a radial narrowing inside the hollow cylindrical element 107, which defines an opening, along the central longitudinal axis of said hollow cylindrical element 107, with sharp edges that can cooperate with the surface of the head of the shutter 108 so as to ensure a perfect seal of said seat 104 when the shutter is in the closed position, i.e. in abutment against the seat of the valve 104.

A spring 109 pushes the shutter 108 with a preset force in the stable closing direction. The shutter 108 is articulated to a lever 110 in a known way, the lever swinging and being controlled by a deformable membrane 111 that forms a part of the outer wall of the casing 106.

An embodiment variation, not shown, provides a lever-holder mouth equipped with an opening inside the hollow cylindrical element 107.

The casing 106 communicates, through an opening, with a suction/exhalation mouth 102, through which the breathable gas inhaled by the user is exhaled inside the casing 106. The suction/exhalation mouth is equipped with a mouthpiece 105.

A discharge outlet is provided on the casing 106 for the exhaled air that is fed into the casing 106 itself through the mouth 102 itself and the suction/exhalation opening. Said outlet is equipped with a membrane-like non-return valve, which opens as the pressure inside the casing 106 increases due to the inflow of gas during the exhalation step and which is kept in closed condition by the very elasticity of the material said non-return valve is composed of.

In the suctioning step, the depression generated inside the casing 106 causes the membrane 111 to push on the lever 110 which acts against the elastic means 109, i.e. the spring, and moves the shutter 108 away from the valve seat 104, in the open position, so that the pressurized gas, from the supply tube 103 can enter the hollow cylindrical element 107 of the reducing device from the inlet 117 and through the valve seat, and escape from an outlet 112 provided on the shell surface of said hollow cylindrical element 107, to which a dedicated supply duct 101, named bypass duct, is connected.

Therefore, the pressure reducing device, having the function of lowering and regulating the pressure of the breathable gas thus adapting it to the ambient pressure, has a valve seat 104 interposed between an inlet for the intermediate-pressure gas (coming from the first pressure-reducing stage) and an outlet, for the reduced-pressure gas, i.e. an opening for communicating with the casing 106.

Said bypass duct, connected downstream of the valve and therefore at or downstream of the outlet, brings the breathable gas directly from the inlet or supply mouth 107 into the suction/exhalation mouth 102, without the gas passing through the casing 106.

According to an embodiment, said outlet leading the gas towards the bypass duct 101 and therefore in the suction/exhalation mouth 102 consists of a side cutout 112 provided in the shell wall of the hollow cylindrical element 107.

As well known, the bypass duct 101 can be either outside the casing 106 (FIG. 34) or integrally obtained in the wall thickness of the casing 106 of said second stage 1 (not shown).

In the embodiments shown as known art, in particular in FIG. 35, said hollow cylindrical element 107 passes through the wall of the casing 106 at a single point at which it is sealingly fastened to the casing 106 and it is connected, with the open end, to the gas supply duct 103, while its length is so as to end, with the other closed end, inside the casing 106 itself.

As illustrated in FIGS. 1 to 3, according to a first characteristic of the invention that can be provided by itself or in combination with the other characteristics shown in the figures, the bypass duct 101 has a connecting section 401 leading into the suction/exhalation mouth 102 through an opening whose axis is oriented in an inclined direction, i.e. converging towards the central axis of said mouth 102. This is shown in FIG. 3. A1 denotes the longitudinal central axis of the mouth 102, while A2 denotes the axis of the outlet of the connecting section 401.

The angle α between said two axes is less than 90° so that the flow fed by the by-pass has a component also in the direction of the gas main flow from the casing 1 to said mouth 102.

According to a further characteristic, the connecting section 401 that connects to the mouth has, along a certain length, a direction coaxial to that of the outlet leading into said mouth, i.e. to the axis A2.

On the other hand, the connecting section 201 that connects the by-pass to the supply duct 107, leads into said duct 107 through an opening whose axis is oriented substantially perpendicular to the axis of said duct 107.

Also as regards the angle β between the direction of the axis A4 of the outlet leading the connecting section 201 into the duct 107, with respect to the axis A3 of said duct, this angle may vary and this variation is preferably expected to be between 75 and 105°.

The illustrated variation provides that the axis A2 of the bypass outlet leading into the mouth 102 and the axis A4 of the bypass outlet leading into the duct 107 are both substantially contained in the same plane containing the axis A1 of said mouth 102 and the axis A3 of said duct 107, respectively, or in a plane immediately adjacent to the plane containing the axis A1 of said mouth 102 and the axis A3 of said duct 107.

The connecting end 201 is linked to the duct 107 by an elbow whose angular extent is equal to the angle β and which is connected to a first straight intermediate section 301, whose axis is oriented parallel to the axis A3 of the supply duct 107, in the direction of the casing 1.

Said straight intermediate section 301 is linked to the section 401 connecting to the mouth 102 with a second intermediate section 601 thanks to two curved sections 501, 701, respectively, having different angular amplitudes of curvature, different directions of curvature and/or possibly also different radii of curvature. Said curved lengths can differ from each other by only one of said characteristics formed in the radius of curvature, direction of curvature and angular amplitude of curvature or by two of them or by all three, and this depends on the shape characteristics of the casing, the mouth 102 and the duct 107.

In an embodiment in which, as in the illustrated one, the various sections 201, 301, 401, 501, 601, 701 of the by-pass duct 101 adhere directly to at least part of the supply duct 107, at least part of the suction/exhalation mouth 102 and at least part of the wall of the casing 1 provided between said duct 107 and said mouth 102, the curved lengths vary depending on the possible configurations of both the size and the shape of the casing, the duct 107 and the mouth 102.

The aforesaid characteristic, which in this case provides that the first intermediate section and the first connecting section, denoted by 201, 301, respectively, adhere to the supply duct 107, while the second intermediate section 601 with the curved lengths 501, 701 adheres to the casing portion between the duct 107 and the mouth 102 and the connecting section 401 adheres to the mouth 102, is particularly advantageous when manufacturing the body of the second stage with plastic material, as it allows the walls of the by-pass to be made in one piece with the walls of the duct 107, the casing 1 and the mouth 102, respectively, thereby making the by-pass very strong compared to known-in-the-art embodiments described above in which the by-pass consists of a tube that is separated from the remaining parts except at the ends to be inserted into the duct 107 and the mouth 102.

While a construction of metal material of the second-stage body allows the by-pass duct to be separately manufactured and then welded to the supply duct 107 and the suction/exhalation mouth 102, respectively, this process cannot be provided in the case of a second-stage body made of plastic material, due to problems of mechanical strength and stability as well as to problems of ensuring the seal of the fastening process.

From the point of view of costs, a second stage with a plastic body is extremely less expensive and can easily be manufactured with respect to a second stage with metal body, so that it is advantageous to be able to provide a method for manufacturing with plastic material said body equipped with a by-pass with a pattern having a plurality of directions of curvature.

A particularly advantageous manufacturing process provides that the body of the second stage is formed by injection molding, while, in order to simultaneously manufacture the by-pass duct with two or more different directions of curvature, a sacrificial insert having at least the shape matching the compartment defined by the by-pass duct is provided.

FIG. 4 shows a first embodiment of the sacrificial insert, which in this case provides an element having the size and shape of the recess or compartment defined by the path chosen for the bypass duct.

As evident, the insert 40 extends inside the mouth 102 and comes out of it with an end 41 which is intended to be gripped by positioning means inside a mold for injection molding.

FIGS. 5 and 6 show a variation of this embodiment in which the insert denoted by 50 consists of three portions. An intermediate portion 150 having the size and shape of the inner compartment of the by-pass duct, a portion 250 fastened to one end of said intermediate portion 150 and having along a certain length and over a certain angular extent, i.e. circumferential, the shape of the supply duct 107, that is a part thereof in which the outlet of the by-pass duct is provided, a further portion 350 attached to the opposite end of said intermediate portion 150 and having along a certain length and over a certain angular extent, i.e. circumferential, the shape of the suction/exhalation mouth 102, that is a part thereof where the outlet of the by-pass duct is provided.

As evident, these end portions 250, 350 have coupling interfaces 450 to be coupled to supports (not shown) consisting, for example, of the mold parts intended to fill the regions of the mold cavity corresponding to the recesses delimited by the walls of the mouth 102 and the duct 107. In order to obtain the tubular shapes of the duct and the mouth, it is necessary that these parts of the mold are present.

FIGS. 7 and 22 show a third embodiment of the sacrificial insert denoted by 70.

FIGS. 8 to 21 and 23 to 30 show different steps in the forming process by injection molding with overmolding of the sacrificial insert 70 according to FIGS. 7 and 22.

As evident from FIGS. 7 and 22, also in this case, the sacrificial insert has three portions, namely the intermediate portion 170 and, at the ends, insert portions 270 and 370 which, unlike the example according to FIGS. 5 and 6, extend substantially along the entire axial length and over the entire circumferential extent of the cavities delimited by the shell walls of the suction/exhalation mouth 102 and the supply duct 107.

According to a possible embodiment variation, the two portions 270 and 370 with the shape and size of the cavities of the mouth 102 and the duct 107 can be made either solid or tubular, as shown in the figures.

In the second case, in addition to saving material, the cavity of the portions 270 and 370 allows the insert to be positioned and held in position thanks to parts of the mold and/or the matched mold that are inserted inside said portions 270 and 370 of the sacrificial insert.

In combination with the above mentioned variations, of the inside 70 it is possible that the part 170 corresponding to the inner compartment of the by-pass duct is also made tubular or more advantageously with a solid cross-section.

All the embodiment variations 40, 50 and 70 of the sacrificial insert can provide that the latter is manufactured by injection molding. As a result, the manufacture of the insert is quick and inexpensive.

FIGS. 8 to 21 and 23 to 30 clearly show the various stages of filling the mold and covering the sacrificial insert.

As evident, at first the plastic material intended to form the suction/exhalation mouth is injected and then the material extends over the by-pass duct and to the supply duct 107.

The by-pass duct is finished at the same time as the forming finish of the remaining parts of the second-stage body.

At the end of the forming process, the body shown in FIG. 30 is obtained.

A washing operation with a suitable solvent removes the sacrificial insert and a reducing second-stage with a body as shown in FIGS. 31 to 33 is obtained.

This figure also shows a variation of the valve operating members which provide a lever 80 which is mounted to swing forward and backward in the direction of the front opening of the casing 1 and which operates the valve shutter by moving it from the closed to the open condition. The lever is mounted over a cylindrical support having lateral openings (not visible) through which inner transverse appendages of the two branches of the fork-shaped end of the lever are subjected to stress by means of an elastic pressure spring.

A screw adjusting the elastic stress onto the lever is located at the end opposite the duct 107. This construction of the valve operating mechanism is also known and common in market-available devices.

As regards the material for manufacturing the sacrificial insert, different plastic materials are possible that can be processed by injection molding to obtain the sacrificial insert. The preferred material is a water-soluble material, as it prevents problems that are related to particular organic solvents and that concern both compatibility with the material of the second-stage body, and safety of the environment and service personnel.

Advantageously, according to still another characteristic, both the injection of the material of the second-stage body and also that for overmolding the sacrificial insert are carried out by means of a plurality of injection nozzles spread along the extent of the sacrificial insert and which are sequentially activated upon the injection of the material according to preset times and patterns of chronological order with respect to one another. 

The invention claimed is:
 1. A second pressure-reducing stage for underwater use, comprising: a supply duct (107) of a breathable gas in which a valve of a pressure reducing device to reduce the pressure of the breathable gas is provided, the valve being interposed between an inlet of said supply duct (107) and a suction/exhalation mouth (102) to suction/exhale said breathable gas; a casing (106) containing pressure-sensitive means to control an opening/closing of said valve, the supply duct (107) and the suction/exhalation mouth (102) leading into said casing and being in communication therewith; and a bypass duct (101) for supplying at least part of a flow of said breathable gas from the supply duct (107) downstream of said valve, directly into the suction/exhalation mouth (102), wherein the by-pass duct (101) joins the suction/exhalation mouth through an opening having an axis oriented in a direction which converges towards a longitudinal axis of said suction/exhalation mouth.
 2. The second pressure-reducing stage according to claim 1, wherein an angle enclosed between an axis (A2) of an outlet of the by-pass duct (101) leading into the suction/exhalation mouth and the longitudinal axis (A1) of the suction/exhalation mouth is less than 90°.
 3. The second pressure-reducing stage according to claim 1, wherein the by-pass duct (101) joins the supply duct through an outlet having a longitudinal axis (A4) oriented at an angle with respect to a longitudinal axis of the supply duct (107) between 75 and 105°.
 4. The second pressure-reducing stage, according to claim 1, wherein the supply duct (107) has the longitudinal axis (A3) oriented according to a first direction and the suction/exhalation mouth (102) has a longitudinal axis (A1) oriented according to a second direction, said first and said second directions being different from each other and crossed to one another, wherein the by-pass duct (101) has a first connecting section (201) to connect to the supply duct (107) with a longitudinal axis (A4) of an outlet leading into the supply duct (107) oriented transversely to a longitudinal axis (A3) of said supply duct (107) with a predetermined incidence angle, the by-pass duct (101) having a second connecting end-section (401) to connect to the suction/exhalation mouth (102), a longitudinal axis (A2) of the an opening leading into said suction/exhalation mouth (102) being oriented transversely to the longitudinal axis (A1) of said suction/exhalation mouth (102) with a second incidence angle, and wherein said first connecting section (201) and said second connecting section (401) of the by-pass duct (101) are connected together through one or more intermediate sections (301, 601, 501, 701) having at least two curvatures with two different radii of curvature and/or according to different directions of curvature.
 5. The second pressure-reducing stage according to claim 1, wherein said casing (1), said supply duct (107), said suction/exhalation mouth (102), and said by-pass duct (101) are made of plastic.
 6. The second pressure-reducing stage according to claim 4, wherein the one or more intermediate sections (301, 501, 601, 701) of the by-pass duct (101) are made to adhere against at least part of an outer wall, at least of the supply duct (107) and/or the suction/exhalation mouth (102) and/or part of an outer wall of the casing (1) provided between the suction duct (107) and the suction/exhalation mouth (102).
 7. The second pressure-reducing stage according to claim 1, wherein walls delimiting the by-pass duct (101), and the supply duct (107) and/or the suction/exhalation mouth (102) and/or the casing, are made of a same material and in one piece.
 8. The second pressure-reducing stage according to claim 4, wherein the first connecting section (201) of the by-pass duct leads into the supply duct (107) with the outlet having the longitudinal axis (A4) perpendicular to the longitudinal axis (A3) of the supply duct (107), and extends with a first straight intermediate section (301) of the one or more intermediate section whose longitudinal axis is parallel to the longitudinal axis of said supply duct (107) and said outlet is connected to said first straight intermediate section (301) with a 90° curvature toward the casing (1), wherein the second connecting section (401) of the by-pass duct (1) leads into the suction/exhalation mouth (102) through the opening, the opening having the opening having the longitudinal axis (A2) oriented at an acute angle with respect to the longitudinal axis (A1) of the suction/exhalation mouth (102) and from which the second connecting section (401) of the by-pass duct (1) branches off, the second connecting section having a longitudinal axis parallel to the longitudinal axis of the opening, and wherein between said second connecting section (401) of the by-pass duct (101) and said first straight intermediate section (301) there is a second intermediate linking section (601) linked to said second section (401) for connection to the suction/exhalation mouth and to the first straight intermediate section (301) with a respective curved length (501, 701), said curved lengths having identical or different directions and/or angles and/or radii of curvature.
 9. The second pressure-reducing stage according to claim 8, wherein the longitudinal axis (A3) of the supply duct (107) extends in a different plane with respect to the longitudinal axis (A1) of the suction/exhalation mouth (102), wherein the longitudinal axis (A21) of the second connecting section (401) for the connection to the suction/exhalation mouth (102) is in a plane coincident with a plane containing the longitudinal axis of said suction/exhalation mouth (102) or whose distance from the plane containing the longitudinal axis of said suction/exhalation mouth (102) is different from a distance of a plane containing the longitudinal axis (A3) of the supply duct (107) and said second intermediate section (601), the longitudinal axis of the second intermediate section (601) having an inclination with respect to said planes, and the curved lengths (501, 701) being made with angular extensions corresponding to said inclination.
 10. A process of manufacturing a second pressure-reducing stage for underwater use equipped with a bypass duct, the process comprising the steps of: providing a sacrificial insert whose shape matches at least an inner compartment of the by-pass duct, placing said sacrificial insert in a mold provided with at least one or more injection nozzles; providing sacrificial positioning supports for said sacrificial insert; and closing the mold and injecting a forming plastic to form a casing, a supply duct, and suction/exhalation mouth portions of the second pressure-reducing stage.
 11. The process according to claim 10, wherein the sacrificial insert (50, 70) is made to match the a shape both of an inner compartment of the by-pass duct (101) and at least part of an inner compartment of the supply duct (107) and/or of a suction/exhalation mouth (102), said sacrificial insert (250, 350; 270, 370) being provided at least over an angular amplitude in a circumferential direction and along an axial length at respective openings leading the by-pass duct (101) into said supply duct (107) and/or into said suction/exhalation mouth (102).
 12. The process according to claim 10, wherein said sacrificial insert (50, 70) comprises a part (150, 170) shaped to match an inner compartment of the by-pass duct (101) and a part (250, 270) of the sacrificial insert matching the entire supply duct (107) and a part (350, 370) of the sacrificial insert matching the inner compartment of the suction/exhalation mouth (102), respectively at ends of said part matching the inner compartment of the by-pass duct (101).
 13. The process according to claim 12, wherein the part (250, 270) of the sacrificial insert matching the supply duct (107) in its entirety and/or the part (350, 370) of the sacrificial insert matching the inner compartment of the suction/exhalation mouth (102), are made tubular.
 14. The process according to claim 10, wherein the sacrificial insert is positioned in a forming mold by using inserts, shaped as protrusions of a mold part inserted either inside a part of the sacrificial insert matching the supply duct (107) in its entirety and/a the part of the sacrificial insert matching an inner compartment of the suction/exhalation mouth in order to obtain a tubular shape of said supply duct and/or said suction/exhalation mouth.
 15. The process according to claim 10, wherein said sacrificial insert is made in one piece by injection molding with a plastic material that is removable by solution.
 16. The process according to claim 10, further comprising a step of providing and arranging a plurality of injection nozzles of a plastic material for forming the casing, the supply duct, the suction/exhalation mouth and the by-pass duct, which are arranged along a length of said by-pass duct.
 17. The process according to claim 16, further comprising the step of supplying a plastic material through the plurality of injection nozzles at different times according to a predetermined time sequence. 